Long ago before the rise of the Crystal Empire there existed the Shadow Empire ruled by a dark beauty of a queen, most of their history lost to time when the Crystal Empire took over their shadowy realm with their brilliant light. Tho their kingdom was lost and sealed beneath the Crystal Empire a few Umbrum managed to escape the fate of the rest of their kind and survive on the fringes of society. Tho now they are no longer true Umbrum, who still reside sealed beneath the Crystal Empire, these off-shoots are still tainted by the darkness of their ancestors. Their appearance, dark coats and manes with glowing red or yellow eyes, frightening and stories of them existing making them out to be more the Equestrian version of the Boogyman. One notable Umbrum found his way back to the Crystal Empire where he was transformed into the Shadow Lord by the remaining power of the Shadow Queen and he tried to take over and rule as a tyrant instead of freeing his ancestors.

FeyMedium+2 Dexterity +2 IntelligenceSpeed 40Quadruped +50% carry weight and +4 CMD vs TripFingerlessDarkvision 60 feetShadow Resistance- Cold Resistance 5 Electric Resistance 5Shadow Blending- Umbrum gain +50% miss chance when in low-light as opposed to the normal 20%Shadow Caster- Members of this race add +1 to the saving throw DCs for their spells and spell-like abilities of the illusion (shadow) subschool.Shadow Magic: Members of this race add +1 to the DC of any saving throws against spells of the shadow subschool that they cast. Members of this race with a Charisma score of 11 or higher also gain the following spell-like abilities: 1/day—ghost sound, pass without trace, ventriloquism. The caster level for these spell-like abilities is equal to the user's character level.Negative Energy Affinity- A member of this race is alive, but reacts to positive and negative energy as if it were undead—positive energy harms it, while negative energy heals it.Language: Common, Equis, Shadow Equis

David wrote:There's not too much there to help them be ultra scary, besides benefitting from being in thematic lighting. Also, did they have cutie marks?

Honestly I don't know, the only Umbrum ever shown in the show is King Sombra. As for them being scary it's more of legends and myths about them that have been passed down over generations. They were thought to be extinct for a long time by the time a young Sombra was discovered outside the Crystal Empire. I think that they're like the other Pony races having a Cutie Mark but have a natural affinity for shadows and darkness (just like Pegasi have an affinity for the weather, Earth-bounds have an affinity for the land, and Unicorns have an affinity with magic) . I could look and see if there's anything else I can add to them to add to their scariness, there were a few more things with the 'Shadow' prefix in them.

Most of that lore I wrote was inspired by the MLP wiki and even then all they had was about a paragraph about them so I added a bit more to it.

Well from what I see some do some don't, you don't even get a good view of Sombras flank even in his good alternate universe appearance. Well any cannon images of him, there are fan images of him with both cutie mark and blank flank.

True... I just looked them up a bit more and they don't look like normal ponies as well. Hm maybe these could be similar to pre-evil Sombra type of Shadow Pony, not the true ones but an off shoot sub-species. Maybe give them the Negative Energy Affinity trait which swaps how they react to Positive and Negative energy, like how Sombra would get ill when in the presence of the Crystal Heart.